U.S. Pat. Nos. 3,808,178 and 4,120,570, issued to N. E. Gaylord in 1974 and 1978 respectively, concerns linear random copolymers of polysiloxanyl and alkyl acrylates and methacrylates which have increased oxygen permeability, as compared to the alkyl methacrylates alone for example. Use of the polymers in contact lenses for correcting visual defects of the human eye is taught. Further modifications of such polymers with an itaconate ester, and preferably including a crosslinking agent and a hydrophilic monomer, are disclosed in U.S. Pat. No. 4,152,508 issued to E. J. Ellis et al. (1979).
U.S. Pat. No. 4,254,248 issued to G. D. Friends et al. (1981) concerns acrylate and methacrylate soft contact lenses using as a comonomer polysiloxanes end-capped with polymerizable unsaturated groups. The copolymers have high tear strengths and a high modulus of elasticity. Such comonomers are also disclosed in U.S. Pat. No. 4,189,546 issued to W. G. Deichert et al. (1980) to make polymeric shaped articles for biomedical applications.
U.S. Pat. Nos. 4,659,782 and 4,659,783 issued to H. J. Spinelli in 1987 teach the preparation of acrylic star polymers with crosslinked acrylic cores and acrylic arms. Such star polymers can contain reactive functional groups, including carbon-carbon double bonds as disclosed in U.S. Pat. No. 4,810,756 to Spinelli (1989). The incorporation of the star polymers into other polymer compositions to give improved properties is disclosed. The use of functionalized star polymers in clear or filled acrylic sheet or castings is referred to in U.S. Pat. No. 4,810,756.
In the prior art, as represented for example by the above Gaylord patents, improvements in one polymer property, such as oxygen permeability, are frequently gained at the expense of another property, such as hardness or machineability. Optical clarity must remain unaffected as well. Improved methods and materials which can provide polymeric contact lens compositions having improved combinations of properties remain highly desirable.
An object of this invention is a novel acrylic star polymer which is compatible with and can be used in polymer compositions for contact lenses to provide improved properties. Another object is a novel star polymer which can be incorporated into polysiloxanyl-, alkyl-(meth)acrylate copolymers during bulk polymerization of the copolymer to provide a novel combination of oxygen permeability and hardness and not adversely affect optical clarity.